Exploratory Chemical Fingerprinting of the Pulp and Peel of Selenicereus setaceus by Positive-Ion Mode Paper Spray Mass Spectrometry

Selenicereus setaceus a native cactus species from the Brazilian Cerrado, remains largely unexplored with respect to its phytochemical composition. This study investigated the positive-ion chemical fingerprints of the pulp and peel of S. setaceus collected from two Brazilian regions using paper spray mass spectrometry (PS-MS), and evaluated the influence of three extraction strategies (maceration, ultrasound-assisted extraction, and Ultra-Turrax homogenization) on the detected chemical profiles. The commercially cultivated Selenicereus undatus was included for comparative purposes. Twenty-five compounds were tentatively annotated based on precursor ions, tandem mass spectrometry (MS/MS) fragmentation patterns, and comparison with previously reported data. Betalains represented the predominant class of detected metabolites, particularly in the peel, where several decarboxylated and dehydrogenated betacyanin derivatives were observed. Flavonoids, phenylpropanoids, benzoic acid derivatives, oligosaccharides, and glycosides were also tentatively assigned. Ions compatible with hesperidin, protocatechuic acid-O-hexoside, and paeoniflorin were detected in S. setaceus, expanding the phytochemical information currently available for this underexplored species. The peel of fruits collected in the Federal District exhibited the highest number of tentatively annotated compounds, highlighting its potential as a source of bioactive metabolites for future valorization. Exploratory multivariate analysis further revealed differences between peel and pulp fingerprints and among extraction procedures, although the overall analytical profiles were broadly comparable. Because the study was restricted to positive-ion PS-MS and compound assignments were based on tentative annotations, the reported fingerprints should be interpreted as exploratory rather than comprehensive metabolomic profiles. Nevertheless, the results demonstrate that positive-ion PS-MS provides a rapid and effective platform for the chemical fingerprinting of underexplored Brazilian native fruits and contributes new phytochemical information on S. setaceus.